I notice some of my points are being discussed already, but I need to brain dump my thoughts. This is going to be a lot to take in at once.
The action in Winter Soldier was the perfect level of grand scale without being overstuffed or overly-frenetic. I wonder how much further Marvel can push it because it went right up to the edge several times here. You can start right at the beginning, which would occasionally go to Bourne style editing, especially during the fight with Crossbones. What were those things on his arms and how did they work? We never get a good look at them. The guy just seemed to have large amounts of firepower coming off both shoulders.
The Russo Brothers do such a good job keeping so many characters engaged in the battles, but I noticed Scarlet Witch and Vision tend to spend more time on the sidelines, appearing for last minute rescues. There's already too much with people leaping and falling from great distances without injury. (There's a moment where Cap gets out of a flipping car that's like something I saw in a hilarious Indian or Turkish film, only here it's better edited.) I like these moments and small doses and when done in a reasonably convincing manner, but here everybody's doing it all the time. Spider-Man survives bone-breaking tosses and Black Panther doesn't even flinch while an attack chopper sprays him with bullets.
Getting back to Vision and Scarlet Witch, they're too powerful for these sequences. I like their relationship, and the way Scarlet is like Elsa in Frozen, so powerful everyone is afraid of her. But when Captain America has her draw all the gas grenade smoke from the building, it's cheating. Might as well drag the men outside too. Seems like most of these battles could've been over instantly with her freezing everyone in place. Meanwhile Vision passes through everything and fires a beam of unknown power, though it seems like it would slice Captain America's shield in half... or Tony Stark if it cared too.
Moving forward I would be all for Vision and Scarlet Witch getting killed. Just to level the field a little. For much of the film there was a feeling that the MCU has reached the point where it could start killing off some characters we care about. The film could've benefitted from some death. But they even back away from Bucky, perhaps the most obvious choice for creating peace through sacrifice. Where's Joss Whedon when you need him?
I get that we're now of an age when we don't want our heroes claiming no responsibility for the death and destruction in battle. This all still seems to be fallout from Man of Steel. But do I want to see action movie being so responsible? I don't like taking events like the epic climax of Avengers Assemble and placing the blame on our heroes for inviting such chaos. The inciting incident with Crossbones is the fault of Crossbones, but Cap even takes the blame for that one.
The genre is becoming self-reflecive in a way I can no longer enjoy. So even during the airport fight, which is completely abandoned, I start mentally calculating the cost of all the smashing. Or during Black Panther's highway chase, I'm now thinking of innocent drivers who suffered injuries and vehicular damage when the overpass came crashing down. This is also going to place extra handcuffs on the writers who must now carefully consider locations for all future battles.
The two Avenger films both suffer by placing the real objective somewhere inside an army of pawns. I like ditching the hoards of similar enemies for smaller character-specific battles. That's partly why the airport battle rocks, we know everyone. They all have weight, which is why it's such a kick to see them have at each other. Even the ones who have never met before. (Hawkeye has a great line about that and almost everyone is surprised by Ant-Man.) The Airport Battle may be the greatest battle the MCU will ever produce. It's the pinnacle of what these films can do. I honestly don't know how they can hope to top it.
Is the motivation for the battle any more grounded than in Dawn of Justice? Their are differences of opinion that have been building for a couple of films now, but these are not characters who will come to lethal blows over these differences. The film hits a point - right around Peter Parker's intro - where the Civil War no longer flows naturally but is meeting the promise made by the poster and title. I don't believe most of these people would choose a side and defend it with force, when they can see the other person's point. There's something false about Hawkeye trading blows with Black Widow while asking, "we're still friends, right?" Spider-Man doesn't have regrets about taking on a legendary Avenger like Captain America? He doesn't even question it? I think the only person looking to actually kill is Black Panther going after Bucky Barnes. So isn't the epic battle more of a Superhero workout? And if that is true, why is there so much lethal force being used? Captain America would have to know about Spider-Man to know what he's doing isn't going to kill the kid. Ant-Man is mucking about in the Iron Man suit, but for all he knows he could pull the wrong wire and kill Stark.
Let's talk about Zemo's plan, and maybe I just need some clarification here. He's trying to find out about the mission back in 1991, but does he already have the surveillance video of the auto crash? It seems that he's had this master plan of turning Cap and Iron Man against each other for a while, but when we first meet him, he's trying to learn about Bucky's mission in 1991. In order for his plan to make sense and for him to have the deep access and knowledge, he would have to know about Stark's father before the film begins.
-- I agree with everyone else that Tom Holland and the MCU take on Spider-Man is really something else. I'm ready to see ho he'll play at feature length. I also think Chadwick Boseman is ready to burn up the screen as Black Panther. I wasn't interested in this character before, but I'm excited to see his solo movie now.
-- The humor, which continues to give Marvel a colossal edge over DC. This may be less joke-filled than Age of Ultron and that's probably a good thing. The airport battle is one of the funniest scenes of the year, but I love the small scenes, like Bucky asking Sam if the seat on the VW moves up. Who would think to give The Winter Soldier some comedy? So nice. Ant-Man is funnier here than in his entire movie.
-- There's debate about whether this is a true Captain America or Avengers 2.5. I think it's as much Iron Man 4 as anything. I'd like to see a screen time clock, because I think Downey gets more than Evans, and he mostly wrestles with the responsibilities of his actions just like in his solo films.
-- I miss S.H.I.E.L.D. It gave Captain America a home base, something he could anchor his patriotism too. The reason why this doesn't feel enough like a Captain America film is there isn't enough of him going on missions for Nick Fury. He's on his own too much, and he's not even conflicted about it. There's too much globetrotting, and America only becomes an important part of a group mission.